Casing hangers are used in oil and gas drilling to suspend casing strings within the wellhead and facilitate the use of an annulus seal between the casing string and the wellhead bore. Annulus seals are the devices that seal the annulus spaces between casing and tubing strings. The present invention relates to an improved casing hanger running tool for use with a casing hanger and wherein the casing hanger is arranged to be secured by an arrangement which is independent of the running tool, such as a clamping arrangement.
Conventional land platform or subsea wellheads use annular seals that are either elastomeric or metal to metal seals. Elastomeric seals are energised by an initial setting squeeze on the elastomer and most metal to metal seals are energised by pushing a sealing element over a taper to expand the seal element until it contacts the wellhead bore and/or hanger outer diameter. These annular seal elements are generally run in conjunction with a casing hanger by means of a casing hanger running tool which also provides the energising force required to set the annular seal via rotation or with pressure assistance. The seals may be an integral feature on the casing hanger and are energised by radially compressing the wellhead housing inwardly in order to squeeze the seal element on the outer diameter casing hanger.
The running tool is released from the casing hanger by rotation of the tool stem relative to the casing hanger. This then enables the running tool to be extracted and removed from the well. The casing hanger running tool is generally required to run or set the annulus seal within the well as well as carrying the casing hanger. Alternatively, the annular seal can be installed as a separate operation, which may be simpler but takes more time.
It is an aim of the present invention to overcome at least one problem associated with the prior art whether referred to herein or otherwise.